Double fluoride of sodium and aluminum and production thereof



Patented Dec. 27, 1949 UNIT ED STATES PATENT ()FFl-CE DOUBLE 'FIJUORIDE0F "SODIUM AND ALU- MI'NUM AND PRODUCTION "THEREOF Daniel C. McLean,-St. Louis, M0,, JohnyE..Mor-

:row, East St. Louis, 111., and-JacohR. .Fox St.

.Louis, Mo., .assignors to Aluminum Company of America, Pittsburgh, 2a.,a corporation of Pennsylvania 1N0 Drawing.-Applicationsseptemhenfi,r1944, rSeriaPNo. 553,284

10 "Claims. (Cl.23'88') This invention relates to the production ofdouble fluorides of sodium .andaluminum, and particularly to theproduction of .sodium aluminum fluoride having improved properties .foruse as an insecticide. Double fluorides of sodium aluminum occurnaturally .as .the minerals cryolite (NazAlFsl and .chidlite, which .hasa reported formula of 5NaF.3AlFs. .The ratio of sodiumfluoride .toaluminum fluoride in the synthetic compound, which isthesubjectofthisinvention, approximates that of cryolite,'bu't underconditions of production may contain these fluorides in .somewhat.difieren-t ratios; 'Consequently, although the compound may .be calledsynthetic .or artificial cryolite, itis lherein described'by the,general term sodium aluminum fluoride, which term fjincludes allimpurities which may be associated withithecompound.

One of theprincipal.uses oidouble fluorideseof sodiumand aluminum, suchas Ithenatural or the synthetic .cryolite,1has Jbeen thatof"insecticidal powder, .and the usefulness of such compounds asstomachand contact poisons -or .various insects hasbeen wellestablished. Whenused-as insecticide the double fluoride of sodium andaluminum must be .in a .rtorm which ,promotfes toxicity and, .inaddition, "must have ,.,physical properties adaptedtc-theiraplica-tion,theiorm of a powder, to .-.-plants, fruit, .foliageandother growingthings. Morrow has. pointed.outiin his U. -S. Patent .No. 2,210,594(patented .Augus't d, 1940) that one physical propertyzofp-prlmarydmportance is properdensity, ifwthe powdered-double aluminumfluoride is to :serve satisfactorily .as either a spraying or dustinginsecticide. ."llhe Morrow :patent also explains that the; propertyofadherence :to the :foliage -or .:-.plant to which the powder :is to beapplied .is aaJSO-flf importance. Thesetand other properties-aregoverning-jactors in the preparation .of .a suitable double sodiumaluminum. fluoride -.-to i be .usedas -a :dust ing insecticide. However,even whenall of .these properties are. attained, .utilization of the.sodium aluminum fluoride .asa dusting insecticide may be limited by.poor .du's'tlng qualities. powdered insecticides .arecften as iswell'lknown, applied by dusting ..methods in winch the dry powder .is..blown..or other-wise released into'lthe atmosphere over theiareacements or foliage ito be treated. and allowed to settle thereon. Inorder to facilitate this dustingoperation, .the powder should havethepropertyof free flow andben0npelleting, i. e., 'theparticles ofthepowdershould not'ball up or stick to leach-other when ejected from the dustingapparatus, Ibut should readily "The ' O'fthe plants and foliage w'illbecovered by'the in .spray m'mtures, "but is expensive.

. microns, and'preferably about 3.5 microns.

insecticide. "It is one of the objectsof this .invention to provide asodium aluminum fluoride product which possesses all iofthese propertiesin high degree, but ,partl-cularlyipossesses properties otfree'flow and'dustibiiityibeyond'those of unconditioned sodium ialuminum fluoridepowders which have beenprev'iouslyj-provided. By unconditlonedj'powders'-we meanthosewhich have not been treated'Wit-h soaps or mineral orvegetableoils' to promote their-flow 'or' their adherence or otherproperties. The addition of such diluents not only induces "the propertyof non-wet- .tability,"which renders-the material unfit for use However,even when such diluentsare used, the combination of "free flowing anddusting properties achieved inthe product of this invention are-notobtained.

"Thenewproduct'ofthisinvention consists of a sodium aluminum fluorideprecipitated form, the particle-size of which is -so controlled thatover 90 per cent., and preferably over 95 per cent., thereof is notgreater than.10 microns in size and the average particle size is"between 2.5 and 5.0 We have discovered "thatin 'so 'faras free flow,nonpelleting and .dustibility "are concerned, while proper :density isuseful, the critical factor'is particle ;size,"and thatLthere is-but anarrow range of :average .particle size in which the sodium aluminumfluoride exhibits theseproperties to'the highest degree and .stillremains within the maximum*toxicity limits'of 0 to *5 "microns. Optimumconditions "are not attained unless atlleast '90 1 per cen'tfof theparticles 'areabout 10 microns, or under, 'in size "or, in other words,the mixing of "a coarse powder .with "a'powder of very minute size, suchas .1 or'2 microns,"-may produce an average particle size-between 2.5and 5.0 microns, without producing in high degree "the ,proper flow anddusting characteristics. .Thus'the average 'particle size must not:only'be within .the range indicated, butthere shouldbeaminimum'oflarger andsm'aller particles. In other words, the: productmustbe unifornflysized.

described are those devised by us for the production of a sodiumaluminum fluoride powder insecticide having the critical particle sizeand distribution above mentioned, but these methods may likewise be usedfor broader purposes, since by their use, as will hereinafter bedescribed, the

size of particles precipitated may be controlled over a rangesubstantially greater than that which is found useful in the productionof our new and novel insecticide product. These methods, whilespecifically different in manipulation and in consistency of result, maybe generically described as a method of producing sodium aluminumfluoride having particles 90 per cent. of which are of the size ofmicrons or less and having an average particle size of 2.5 to 5.0microns, which comprises neutralizing a sodium aluminum fluoridesolution in the presence of seed particles of a size of 1 to 2 microns,the ratio of the weight of said seed to the weight of soluble fluorine(F2) in the solution being between about 0.45 and 0.87.

The preferred method of controlled precipitation is one by which theproduct of this invention can, if desired, be consistently produced. Inthis process we start with a solution of cryolite and dilute causticsoda or with a solution of sodium aluminum fluoride. In any event, thesolution contains sodium, aluminum, and fluorine and dilute causticalkali. In this solution the content of the aluminum, calculated asalumina, should be the theoretical equivalent of that amount necessaryto form with the fluorine content of the solution the compound NaaAlFs.An excess of alumina may be used, a limiting factor being the purity ofthe final product, since the excess precipitates as aluminum hydrate andconsequently acts as a diluent. Preferably, when an insecticidal sodiumaluminum fluoride is being prepared, the excess should be limited, astrial may indicate, to allow production of a product containing 85 percent. by weight, or more, of sodium aluminum fluoride. To this solutionwe then add a predetermined quantity of sodium aluminum fluorideparticles of predetermined size,and after thoroughly agitating themixture of the solution and these particles to insure uniformdistribution of the particles therein, we neutralize the mixture asquickly as possible. The neutralizing agent may be any compound whichwill neutralize the caustic solution and start the precipitation of thedouble fluoride of sodium and aluminum therefrom, such as, for example,a mineral acid, sulfur dioxide, a soluble bicarbonate or carbon dioxide.During this neutralization step the temperature of the solution shouldbe maintained at about 6 to 140 F., the upper portion of the temperaturerange being used if it is desired to precipitate a product with aminimum content of aluminum hydrate, i. e., about 6 per cent. or less.To produce a precipitate of a particular average particle size in theoperation of this process, the ratio of the amount of solid sodiumaluminum fluoride particles added to the starting solution is adjustedwith reference to the soluble fluorine content of the solution and, inaddition, the average size of the added particles is carefullycontrolled. To produce the preferred product of this invention, 1. e., asodium aluminum fluoride having particles per cent. of which are a sizeof 10 microns or less and having an average particle size of 2.5 to 5.0microns, the solid sodium aluminum fluoride, usually in the form of aslurry containing about 15 per cent. by weight of suspended solids,should be added to the solution in the form of particles having anaverage size of 1 to 2 microns, and the ratio of Weight of the seed tothe soluble F2 in the solution should be between 0.45 and 0.87. Theparticular ratio desirable depends for the most part on the size of theseed particles and the particular size of product sought. Thus, if theseed is of a size of 1 micron and the average size of particleultimately desired is 2.5 microns, the ratio of weight of seed to weightof soluble F2 in the solution will be about 0.80. Other factors beingthe same, an increase in the size of the seed to 2 microns willnecessitate a change of the ratio from 0.8 to 0.87 in order to producethe same average particle size. If an average particle size of 5 micronsis desired, the use of a seed size of 1 micron will require a ratio ofweight of seed to weight of soluble F2 of 0.45, and if the starting sizeof the seed is 2 microns, the ratio must be changed to about 0.56 tomaintain the average size of the particles produced at 5 microns.

Thus, if the average size of the seed employed is 1.5 microns, and afinal product having an average diameter of 2.7 to 3.7 microns isdesired, a ratio of Weight of seed to weight of soluble F2 of 0.675 isneeded. On the other hand, if the seed is 1 micron in size, the ratio ofweight of seed to weight of soluble F2 should be changed to about 0.6 toproduce a final product of the size men tioned, whereas with seed 2microns in size the ratio needed for producing the same product is about0.75. When such conditions are followed the precipitate contains sodiumaluminum fluoride of the particle size desired, and the new product willbe consistently produced. However, in

the preferred use of this process to produce the.

product of this invention, the average particle size of the solid sodiumaluminum fluoride added to the starting solution is maintained at about1 to 2 microns, and the particles are added in the ratio of roughly0.675 pound of particles to each pound of soluble fluorine in thesolution.

A further variation of this process of our invention will, we havediscovered, tend to increase the positive control of the quality of theprecipitate of sodium aluminum fluoride. This modification consists infirst providing a solution containing the soluble fluorine, i. e., asolution containing sodium and fluorine, then adding the amount of solidsodium aluminum fluoride particles desired, and then completing thepreparation of this starting solution by adding the required amount ofcaustic and aluminum compound, i. e., a solution containing sodium andaluminum in alkaline form to adjust the aluminum content of the solutionto the finally desired content. Thereafter the neutralization andprecipitation of the solution proceed as described.

The use of the above described process need not, however, be confined tothe production of the particular products of this invention, but may beused to produce controlled precipitates of other sizes. For instance, ifit is desired to produce a sodium aluminum fluoride product, 90 percent. 01 the particles of which are 5 microns or less in aseacso 5 size,this can be achieved by doubling approxi mately the :quantity :of sodiumaluminum fluoride seed particles added to the starting solution.Likewise, the sodium aluminum'fluoride :produced may be controlled sothat .90 per cent. -;of its particles are greater than :10 microns byadding to the starting solution, in the ratio :Zof about 0.675 pound perpound of soluble fluorine, solid particles of sodium aluminum fluoridehaving an average :size of 8 microns or larger. 7

As an example of the operation of the practical form of process underplant conditions, we will cite an instance of production of the productof this invention. 3200 cubic :feet of solution containing 11 grams perliter of soluble F2 and 3 grams per liter of A1203 were :pumped into atank which wasso constructed that carbon dioxide gas could be fedtherein. To this so'lution was then added 1500 pounds of solid sodiumaluminum fluoride particles having an average particle size of 1.5microns. Next there wasadded to the solution an amount of sodiumaluminate liquor, such as that produced :in the Bayer process, as wouldadjust the A120 .content of the total solution to 4.9 grams per liter.The total mixture was then thoroughly agitated for 30 minutes with airto achieve .complete mixture of the components, and meanwhile thetemperature of the solution was adjusted to 100 F. Thereafter a streamof carbon dioxide gas was forced through the solution and gassing wascontinued until at least 50 per cent. of the sodium hydroxide and sodiumcarbonate present in solution had been converted tosodium bicarbonate.The precipitate obtained was .then separated from the solution by passini.

it througha filter press, the precipitate dried and, because it was inan agglomerated state, the agglomerates were broken down to theirultimate size in a .disintegrator consisting of two sets of circularlyarranged spokes revolving in opposite directions. Upon measuring, theparticles of the product were .found to be distributed according to thefollowing sizes:

Per cent to .5 microns 43.04 to microns 53.7.8 10 to 20.mlcrons 2.46 tomicrons 0.40 Plus 40 microns 0.32

andhad an average particle size of 2.70 microns.

The sodium aluminum fluoride particles which are added to the startingsolution in the above described process may be made in the size desiredby any convenient method. For instance, they might be reduced fromlarger particles by grinding, or they maybe the result of selection, byan air :elutriation method or other method, of :a fraction of theprecipitate produced by the operation of the process. We have found itconvenient, when an average particle size of 1 to 2 microns is required,to produce these particles by treating a sodium aluminate solution withhydrofluoric acid'gas but the method of reducing the sodium aluminumfluoride particles to proper size forms nopart of this invention.

The second and different method of precipitation which will produce theproduct of this invention will now be described. This process, howeveruseful it may be for the'precipitation of an ordinary quality of sodiumaluminum fluoride for insecticidal or other purposes, such as, forinstance, those insecticide powders which are applied to plants orfoliage "in suspension in a liquid or by means other than dusting, isnotthe preferred-methodof producing the specific process.

dusting powder lherein described, because it is not as susceptible toclose :control of size :of the precipitate produced :as is the preferredand first described process.

This second :process comprises the use of a starting solution ofan:acidisuchzas mineral acid, acid carbonate or the :like, which willneutralize an alkaline solution containing sodium, alum-is num, andfluorine .to precipitate therefrom the sodium aluminum fluoride. Thissolution usually contained in some suitable receptacle such .as a tank.Prior to use in the process, it is adjusted to a temperature of at leastand usually to temperatures :in the range of to 100 F. Highertemperatures :may be used but are not usually necessary. Anothersolution such as described .in connection with the first method andcontaining aluminum, fluorine, sodium, and dilute caustic alkali, whichlatter, :of course, may desirably be .sodium hydroxide, is added :to thestarting solution and while this addition takes place more acid oracid-forming material "is added to the starting solution, the :acid inthe starting solution.andathe'addedacid .onacid-forming substance beingadjusted in amount to neutralize about 28 per cent. of the totalincoming caustic solution of sod ium,.aluminum=and fluorine. Theresultant initial precipitate is finely :divided sodium fluoride ofabout 1.5 micron size. During subsequent further neutralization ofsodium aluminum fluoride solution this precipitate then functions in thesame manner as the solid par-'- ticles which were added .from an outsidesource as described previously under the first process, sufflcientsolution containing sodium, aluminum, fluorine, and caustic alkali beingemployed to provide the ratios of weight .of the precipitate formed asdescribed .above to soluble fluorine as are set forth'in connection withthe first method described.

We have found that this process can be "operated to produce our :new andimproved product, i. e., a sodium aluminum fluoride powder havingparticles per cent. of which are not more than 10 microns in size andwhich have an average size of 2.5 to 5.0 microns, 'butincommercialproduction this process is sensitive and the new product isnot always produced. In the manipulation of this second process to thisend, the starting solution is composed of a'solution -:of sodiumbicarbonate containing thatsubstance amounts of at least 30 grams perliter. As will be later explained, this solution can be convenientlyobtained as a by-product of the operation of the The solution is placedin a receptacle, usually a tank, which is provided with means .fordelivering carbon dioxide gas to the solution. The temperature of thesolution is maintained throughout the process at thetem'peratures abovedescribed. Carbon dioxide gas is now fed through the solution andsimultaneously "there is added to the starting solution a solutioncontaining sodium, aluminum, fluorine and caustic alkali. Gassing of thestarting solution with carbon dioxide is continued during and after theaddition to this solution and is continued until the total bicarbonatecontent of the mixed solution is at least 20 grams per liter. Thesolution containing sodium, aluminum, fluorine, and alkali should beadded as quickly as possible to the .startingsolution, preferably at arate of about .60 cubic feet a minute, but this rate :may be as high ascubic feet per minute without substantially affecting the result. Iftheseconditions are closely followed, the result will be, in mostcases,the

precipitation of the new product above described but, even under thebest operating conditions, this product will not always be produced andthere will be batches of precipitate produced which are of difierentaverage particle size and which, while not having the best dustingcharacteristics, may still be used for insecticidal purposes. As aspecific example of the operation of this process, we will cite anexample of the process in production. About 530 cubic feet of a solutioncontaining about 35 grams per liter of sodium carbonate were placed in atank and treated by passing carbon dioxide gas therethrough until thebicarbonate content of the solution was about 35 grams per liter.Thereafter, and while gassing of the starting solution continued, therewas added to the tank at the rate of about 60 cubic feet per minute 2700cubic feet of a caustic solution containing 10 grams per liter offluorine (F2), 4.5 grams per liter of alumina. After the addition ofthis solution, gassing with carbon dioxide was continued until thebicarbonate content of the total solution rose to 25 grams per liter.During this treatment a finely divided free-flowing sodium aluminumfluoride was precipitated. This fluoride was filtered from the solutionin a filter press, dried and treated to eliminate agglomerates.Measurements showed that the resultant powder mass had an averageparticle size of 2.8 microns, that 69.6 per cent. of its particles wereto 5 microns in size, that 28.3 per cent. of its particles were 5 tomicrons in size, that 0.1 per cent. of its particles were 10 to 20microns in size, that 0.1 per cent. of its particles were 20 to 40microns in size and that 1.9 per cent. of its particles were plus 40microns in size. After the removal of the precipitate, 530 cubic feet ofthe mother liquor, from which the precipitate was removed, were returnedto the process and were there treated with carbon dioxide gas to formthe starting solution for the production of the next batch of theprecipitate.

The solution which is added to the starting solution in this process maybe made in any convenient manner. Preferably it should always contain 9to 12 grams of fluorine per liter or more and its alumina content shouldrange between 2 and 4 grams per liter. An excess of alumina above thatrequired to form the compound NazAlFe may be used, but if the finalsodium fluoride precipitate is to contain a minimum amount of excessaluminum hydrate, simple trial will determine how much excess aluminacan be tolerated in this solution without inducing a precipitation ofmore aluminum hydrate in the final product than is desired.

Having thus described our invention, we claim:

1. A free flowing, non-pelleting, dustible insecticide powder composedof sodium aluminum fluoride in originally precipitated form withoutfurther reduction in size, 90 per cent. of the particles of which are insize not greater than 10 microns and which have an average particle sizebetween 2.5 and 4.5 microns.

2. A free flowing, non-pelleting, dustible insecticide powder composedof sodium aluminum fluoride in originally precipitated form withoutfurther reduction in size, 95 per cent. of the particles of which are insize not greater than 10 microns and which have an average particle sizebetween 2.5 and 4.5 microns.

3. The method of precipitating from an alkaline solution containingsodium, aluminum and fluorine values, sodium aluminum fluoride in theform of a precipitate, per cent. of the particles of which are 10microns or less in size, and having an average particle size of 2.5 to5.0 microns, which comprises forming a suspension of sodium aluminumfluoride seed particles of a size between 1 to 2 microns in saidsolution and there-. after neutralizing said solution, said processbeing further characterized by the fact that the ratio of the totalweight of said seed particles to the total weight of soluble fluorine inthe solution is not less than about 0.45 nor greater than 0.87.

4. The method of producing sodium aluminum fluoride in the form ofparticles having an average particle size of from 2.5 to 5 microns, atleast 90 per cent. of said particles being 10 microns or less in size,which comprises forming a suspension of sodium aluminum fluoride seedparticles of a size of from 1 to 2 microns in a solution containingsodium, aluminum, and fluorine values, and thereafter precipitatingsodium aluminum fluoride on said seed particles, the ratio of the totalweight of said seed particles to the total weight of the fluorineprecipitated in said precipitation operation being not less than 0.45nor greater than 0.87.

5. The method of producing sodium aluminum fluoride in the form ofparticles having an average particle size of from 2.5 to 5 microns, atleast 90 per cent. of said particles being 10 microns or less in size,which comprises forming a suspension of sodium aluminum fluoride seedparticles of a size of from 1 to 2 microns in an alkaline solutioncontaining sodium, aluminum, and fluorine values, the ratio of the totalweight of seed particles to the total weight of soluble fluorine in thesolution being not less than 0.45 nor greater than 0.87, and thereafterneutralizing said solution.

6. The method of producing sodium aluminum fluoride in the form ofparticles having an average particle size of from 2.5 to 5 microns, atleast 90 per cent. of said particles being 10 microns or less in size,which comprises forming a suspension of sodium aluminum fluoride seedparticles of a size of from 1 to 2 microns in a solution containingsodium, aluminum, and fluorine values, and thereafter precipitatingsodium aluminum fluoride on said seed particles, the ratio of the totalweight of said seed particles to the total Weight of the fluorineprecipitated in said precipitation operation being not less than about0.6 nor greater than 0.75.

7. The method of producing sodium aluminum fluoride in the form ofparticles having an average particle size of from 2.5 to 5 microns, atleast 90 per cent. of said particles being 10 microns or less in size,which comprises forming a suspension of sodium aluminum fluoride seedparticles of a size of from 1 to 2 microns in a solution containingsodium, aluminum, and fluorine values, and thereafter precipitatingsodium aluminum fluoride on said seed particles, the ratio of the totalweight of said seed particles to the total Weight of the fluorineprecipitated in said precipitation operation being about 0.675.

8. The process of claim 4 characterized by the fact that the seedparticles are added to the solution.

9. The process of claim 4 characterized by the fact that the seedparticles are formed in the solution by precipitation prior to finalneutralization.

10. A free flowing, non-pelleting, dustible in-'- secticide powdercomposed of sodium aluminum fluoride in originally precipitated formwithout further reduction in size, 90 per cent. of the particles ofwhich are in size not greater than 10 microns and which have an averageparticle size between 2.5 and 4.5 microns, said sodium alumi numfluoride being the product of neutralization in the presence of sodiumaluminum fluoride seed particles of a size between one to two microns,of an alkaline solution containing sodium aluminum and fluorine valuesunder conditions where the ratio of the total weight of the said seedparticles to the total weight of the sodium in the solution is not lessthan about 0.45 nor greater than 0.87.

DANIEL C. MoLEAN.

JOHN E. MORROW.

JACOB R. FOX.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Certificate of Correction Patent No. 2,492,650December 27, 1949 DANIEL C. McLEAN ET AL.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows:

Column 7, line 51, before the word fluoride insert aluminum; and thatthe said Letters Patent should be read with this correction therein thatthe same may conform to the record of the casein the Patent Oflice.

Signed and sealed this 16th day of May, A. D. 1950.

THOMAS F, MURPHY,

Assistant Oommz'ssioner of Patents.

